Fish of Montgomery County

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Montgomery County is home to more than 60 species of freshwater fish, representing nearly every family of freshwater fish known in Maryland. This includes trout, catfishes, sunfishes and bass, minnows, suckers, sculpins, darters and perch, killifishes, lampreys, American eel, Eastern mudminnow, and Eastern mosquitofish.

Fish are important to Montgomery County stream ecosystems. They are part of our natural history, provide food, recreation and have intrinsic and economic value. Fish also play a vital ecological role in the overall food web. County biologists study fish communities to provide insight on the health and condition of County streams.

Fish Species

Montgomery County divides fish into three groups based on their ability to survive in polluted waters. Sensitive fish are only able to survive in the county's highest quality streams. Moderately tolerant fish can survive and sometimes thrive in areas that receive minor pollution. Tolerant fish live in most streams in the county, but they are the only fish that can survive in heavily polluted waters.

Fish provide scientists insight into past stream conditions. When a stream is stressed, fish communities respond over time. Streams stressed by excessive sediment have less desirable habitat and lose sensitive fish species like Blueridge Sculpin.

If the water is polluted, then fish may develop lesions or may have physical deformities.

Blueridge Sculpin

Deformed Green Sunfish

Monitoring and Data

Stream biologists study fish species and any changes in their population size over time, because fish serve as biological indicators of water quality.

Most fish species have long life spans (2 to 10 years or more) and can reflect both long-term and current water resource quality.

Fish continually inhabit the receiving water and integrate the chemical, physical, and biological histories of the waters.

Since different fish species have varying tolerances to pollution, we can characterize stream water quality based on the presence or absence of pollution-tolerant or pollution-intolerant species.

Fish represent a broad spectrum of community tolerances from very sensitive to highly tolerant and respond to chemical, physical, and biological degradation in characteristic response patterns.

Fish have large ranges and are less affected by natural microhabitat differences than smaller organisms such as benthic macroinvertebrates. This makes fish extremely useful for assessing regional conditions.

What Data Does DEP Collect?

Fish IBI Metrics

Once numbers of individuals are summed for each species present at a stream site, a fish Index of Biotic Integrity (IBI) is calculated based on multiple metrics. The IBI is used to rank the stream in relation to reference stream conditions. To use biological data properly, water resource analysts generally compare the fish data (actually not the raw data but a multi-metric index based on the data) from the stream sites under study, to indices from stream sites in ideal or nearly ideal condition (often called a reference condition). Stream sites are then ranked against the reference condition. This helps DEP set priorities for watershed restoration and improvement.

The fish IBI is averaged with the benthic macroinvertebrate IBI to determine overall stream conditions.

Fish IBI metrics are listed below. A technical, peer-reviewed methodology is used to take raw data and develop them into an acceptable Stream Rating score.

Fish IBI Metrics

Total number of species

Total number of riffle benthic insectivore individuals

Total number of minnow species (cyprinidae)

Total number of intolerant species

Proportion of tolerant individuals

Proportion of individuals as omnivores/generalists

Proportion of individuals as pioneering species

Total number of individuals (excluding tolerant species)

Proportion of individuals with disease/anomalies

Montgomery County has tabular raw fish data and fish narrative summaries from 1994-present for most monitoring sites around the County. Also available are GIS coverages (or maps) showing fish conditions. Maps can be developed to order depending on the request. Submit a request for either raw data or data in maps.

The following tables provide an explanation of the datafields found in our raw tabular data:

Fish Data Table

Field Name

Description

STATION

The station field is a nine character code that identifies the station name. The stations are a combination of the two letter code for the watershed+the two letter code for the subwatershed+ the single digit stream order code+ the sequential reach number.

SPECIES

The official common name of the fish species collected during sampling.

SAMPLE_DATE

The date the station was sampled.

PASS1

Number of specimens collected from the first sampling pass.

PASS2

Number of specimens collected from the second sampling pass.

ANOMALIES

The total number of anomalies.

ANOMALIES_TYPE

The number of anomalies found of a certain type + the two letter code for the type of anomaly found.

Fish Narrative Table

Field Name

Description

STATION

The station field is a nine character code that identifies the station name. The stations are a combination of the two letter code for the watershed+the two letter code for the subwatershed+ the single digit stream order code+ the sequential reach number.

DATE

The date the station was sampled.

SUMMARYSCORE

The final IBI summary score (1-5).

NARRATIVE

Descriptive word to describe the condition of the stream in relation to reference streams. Narratives are either Excellent (>4.5), Good (3.3-4.5), Fair (2.2-3.2), or Poor (<2.2).